We see a lot about Corrosion Under Insulation (CUI) as it relates to piping, but we can not forget that the same failure mode can occur on vessels as well. API 510 spells out some ranges as to when we MUST consider the need for a CUI inspection on our vessel(s).
CUI Inspections must be considered for (Section 5.5.6.1) carbon steel and low alloy operating between 10°F and 350°F and stainless steel operating between 140°F and 400°F. These CUI inspections can be performed by an inspector or other qualified personnel (i.e. same as external). Susceptible locations include:
- Insulation or stiffening rings
- Nozzles and manways
- Structural penetrations (ladder clips, pipe supports, etc)
- Damage insulation
- Insulation with failed caulking
- Top and bottom heads
CUI inspection(s) may require some or all insulation be removed. However, insulation removal MAY NOT be necessary if:
- Insulation is in good condition and there is no reason to suspect damage behind the insulation;
- CUI inspection can be performed with UT from ID of vessel